1. Field of the Invention
The present invention relates to a controller of a common rail fuel injection system for performing feedback control of fuel pressure.
2. Description of Related Art
In a common rail fuel injection system, a fuel pump pressure-feeds fuel and a common rail accumulates the fuel at high pressure corresponding to fuel injection pressure. The fuel accumulated in the common rail is injected and supplied into an engine through fuel injection valves. The common rail is provided with a fuel pressure sensor, which senses actual pressure of the fuel. The fuel pressure feedback control is performed to conform the sensed actual pressure to target pressure determined based on operation information of the engine. In the fuel pressure feedback control, a suction control valve provided at a suction section of the fuel pump is driven and controlled to regulate a fuel amount pressure-fed to the common rail, for example, as described in JP-A-2002-276500.
Generally, in the fuel pressure feedback control, a proportional term, an integral term and a differential term of a control amount of the drive control of the fuel pump are calculated based on the pressure deviation of the actual pressure with respect to the target pressure. Specifically, the differential term is calculated in accordance with a fluctuation tendency of the pressure deviation. The differential term has a predictive effect with respect to the change of the target pressure. The differential term is effective in improvement of following performance of the actual pressure in the case where the target pressure rapidly changes or improvement of a phase lag in the case where the target pressure cyclically fluctuates, for example.
However, due to an operation delay in a control object with respect to a control output or transport delay of the fuel through a fuel pressure-feeding pipe, a temporal deviation is generated between the time when the calculated control amount is outputted to the fuel pump and the time when the calculated control amount is sufficiently reflected in the actual pressure. Therefore, in the case where the change tendency of the target pressure changes in accordance with the operation condition of the engine, there is a possibility that reliability of validity of the control amount disappears and the actual pressure exhibits an unintended behavior due to an influence of the differential term calculated as of the change. No problem is caused if the influence of the differential term is absorbed by the other parameters of the proportional term and the integral term. However, the influence of the differential term increases and the other parameters cannot absorb the influence of the differential term specifically in the case where the pressure deviation rapidly changes in accordance with the target pressure. Aimed and suitable fuel injection to the engine cannot be performed if the actual pressure exhibits an unintended behavior. As a result, particulate matters or nitrogen oxides contained in exhaust gas will increase or an abnormal noise will be caused.